In the current funding we found that although NK cells reconstitute in high numbers early after allogeneic transplant, they display diminished killer immunoglobulin receptors (KIR), they are hypo-responsive and poorly kill tumor targets. Using in vitro development models, we also found that the acquisition of KIR and full effector function can be induced by IL-15. The overarching hypothesis of this Project is that NK cells early after hematopoetic transplantation are uneducated and that NK cell education is developmentally regulated by IL-15, activating receptors (2B4 Tim-3), and inhibitory receptor (KIR, NKG2A, LIR-1) ligation, all of which play a role in determining whether AML targets are killed. Promising results from Project 1 ofthe current funding show that allogeneic hematopoietic cell transplantation with favorable KIR B haplotype donors (enhanced by a higher B content score and a Cen-B/B pattern) results in protection from AML relapse. In a second strategy (Project 3), a platform for NK cell adoptive transfer has been established. To improve on existing methods, the NCI has recently developed a cGMP process for production of rhlL-15 which will be made available to the Extramural community. SAI will test IL-15 as part of a novel strategy to expand adoptively transferred adult NK cells. A second course of IL-15 will be given on Day +42 to educate NK cells that reconstitute from CD34+ stem cells from the same donor. In SA2, we will investigate whether KIR immunogenetics determines NK cell function (the favorable Cen-B/B pattern found clinically) and whether IL-15 responsive KIR promoter elements control transcriptional regulation to form the KIR repertoire. SA3 will evaluate a novel activating receptor expressed on most NK cells, Tim-3, which is upregulated by IL-15. We hypothesize it plays a role in NK cell education by upregulating the SAP adaptor (also IL-15 responsive) for 2B4. Tim-3 and 2B4 can directly recognize Galecfin-9 (Gal-9) and CD48 expressing AML targets or may indirectly receive activating signals from dendritic cells that express the same ligands. At completion of these studies, we expect to change practice of NK cell adoptive transfer by use of IL-15 and to inform us about IL-15 mechanisms to induce NK cell education and recognition of AML targets.